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Porpoise Deaths Remain Unexplained

August 4, 2008

Numerous porpoise deaths in Northern California have confused researchers. 

According to scientists, the month of August may see more of the dead mammals wash onto beaches.

Nearly 24 dead porpoises have appeared on California beaches since May. A majority of the cases have been diagnosed as asphyxiation, trauma, pneumonia, malnutrition, and maternal separation, but eight of the deaths remain unexplained.

“This is the time period every year where we do see porpoises and dolphins washed up ashore, it does happen,” said Jim Oswald, spokesman for the Mammal Center in Sausalito. “There are a few more numbers this year.”

The carcasses are being tested for domoic acid poisoning that can be caused by toxic algae in the Pacific Ocean. The poison can cause neurological damage in marine mammals.

The Mammal Center has researched the algae problem since 1998, and discovered that sea lions often pass the poison along to their unborn offspring.

“We want to take a look and see if that’s possible (in harbor porpoises) — is that occurring here?” Oswald said.

According to the National Marine fisheries Services, 13 harbor porpoise deaths occurred in 2007, and 26 in 2006.

Each year the Marine Mammal Center saves nearly 800 injured, or orphaned marine mammals along the California shoreline.  They rehabilitate them, and return them to the wild when they are well.

Harbor porpoises, which are found in the North Pacific and Atlantic waters off the U.S. coast, stay close to shore and feed on fish, squid, and crustaceans in shallow water.

In 2003, Naval sonar exercises were investigated for causing 11 harbor porpoise deaths.  The National Marine Fisheries Services eventually concluded that the porpoises had not suffered from acoustic trauma, but 5 were found to have died from blunt-force trauma.  The other six deaths are still unexplained.

In 2007, the World Wildlife Foundation and the Whale and Dolphin Conservation Society reported that rising ocean temperatures could be a threat to marine mammals.  Climate change could lead to increased toxic algae, lower conception rates, and lower populations of krill, which is primary food source for marine mammals.

The report found that these new threats are in addition to current threats like commercial fishing nets, and pollution.

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